The reactions of 2,4-bis(4-methoxyphenyl)-1,3-dithio-2,4-diphosphetane-2,4-disulfide (Lawesson’s Reagent, LR) with benzylamine (BzNH₂) and 4-phenylbutylamine (PhBuNH₂) yield benzylammonium P-(4-methoxyphenyl)-N-benzyl-amidodithiophosphonate (BzNH₃)(BzNH-adtp) and 4-phenylbutylammonium P-(4-methoxyphenyl)-N-(4-phenylbutyl)-amidodithiophosphonate (PhBuNH₃)(PhBuNH-adtp). The relevant nickel complexes [Ni(BzNH-adtp)₂] and [Ni(PhBuNH-adtp)₂] and the corresponding hydrolysed derivatives (BzNH₃)₂[Ni(dtp)₂] and (PhBuNH₃)₂[Ni(dtp)₂] were prepared and fully characterized. The antimicrobial activity of the aforementioned amidodithiophosphonates against a set of Gram-positive and Gram-negative pathogen bacteria was evaluated, and [Ni(BzNH-adtp)₂] and [Ni(PhBuNH-adtp)₂] showed antiproliferative activity towards Staphylococcus aureus and Staphylococcus haemolyticus strains. density functional theory (DFT) calculations were performed to shed some light on the activity of reported compounds related to their tendency towards P–N bond cleavage.